Dysfunction of osteoclasts leads to pathological bone loss associated with diseases including rheumatoid arthritis, periodontal disease, osteoporosis and metastatic bone tumors. Signal transduction by a group of enzymes called phosphatidylinositol 3-kinases (PI 3-kinases) is known to be crucial for regulating osteoclastic bone resorption. Members of three distinct classes of PI 3-kinase are expressed in osteoclasts. The classes differ in structure, substrate specificity and targeting elements. They are thought to play distinct physiologic roles, although these divisions are not yet clear. To date, few data are available about the precise role of each type of PI 3-kinase in osteoclasts. The central hypothesis of this study is that the PI 3-kinases have non-identical regulatory roles in osteoclasts. An effective antisense to an isoform of a subclass of the class I PI 3-kinase (p110alpha) has been expressed in mature osteoclasts by adeno-associated virus (AAV) based gene transfer techniques. The current proposal has three specific Aims. First, the extent and specificity of the p110alpha knock down will be confirmed. If necessary, additional knockdown approaches will be utilized. Second, the effects of knocking down expression of p110alpha on cytoskeletal organization, cell polarity, osteoclast number and bone resorption will be examined. Finally, the effects of knocking down expression of p110alpha on osteoclast survival and apoptosis will be determined. In summary, by knocking down expression of p110alpha and characterizing the effects using assays for the development, activity and survival of osteoclasts, we should be able to assign specific roles for this enzyme. These studies could lead to the development of new, specific, bone active pharmaceuticals with the potential to improve dental health.